- Local time
- 4:32 PM
- Apr 16, 2014
- Omaha, Nebraska
The threads of the plug protruding into the head is why I prefer to run bpmr7a plugs in my Phantom. The thread body is shorter and sits flush with the chamber while the electrode is projected back into the chamber. I run one step colder due to the projected electrode, which tends to behave a bit hotter than a standard one. These are the same plugs stihl uses in their saws so they are also shorter overall and fit tight frames better.I’ll try gapping the stock z4c and NGK br5hs I have to .025 they’re both at around .018 now/ out of the box. I’ll probably keep the stock plug in til I can get a good read on the plug then switch to the ngk I have and see how it looks eventually and whether or not I need to change to a different heat range.
I generally like running a slightly warmer day plug depending on what the engine is happy with.
I may play with the jetting a little more and see if I can get it running a bit smoother.
If I noticed the stuttering again I will keep that in mind. I was planning to adjust the jetting some more anyway.
I actually just got back in from a short ride though, and the stutter is alot less noticeable after gapping the stock z4c spark plug earlier this morning from .018 to .024 while comparing it to the BR5HS I have because I was curious what heat range it was ( seems it’s about a 7 by NGK standards)
I chose the warmer side of “the middle range” as I’ve always preferred/ had good experiences with a warmer plug. In the case of this engine it seems my instincts paid off, after reading the spark plug, it seems I need a warmer plug and the BR5HS should be just right. I will see when I eventually run/ read it.
I will probably stick with the stock plug for the rest of this first tank of gas.
One thing I noticed is the stock spark plug has a shorter reach than the NGK which protrudes a past the threads into the combustion chamber.
To my knowledge the the spark plug threads should be flush with the female threads of the head, not protruding or recessed…
NGK’s spark plug chart says H plugs are 12.7mm reach L plugs are 11.2mm reach which after checking the z4c is closer to the correct length. I have not looked extensively but it seems there is a NGK B5L B6L etc. that should have the correct thread reach which are pretty standard copper core/ nickel electrode. Don’t know if there is a resistor version.